Complementary metal-oxide semiconductor (CMOS) image sensors are increasingly being used in the commercial market due to their ease of integration, low cost and reduced power consumption.
An image sensor may be fabricated to have a large number of identical sensor elements (pixels), generally more than 1 million, in a (Cartesian) square grid. The pixels may be photodiodes, or other photosensitive elements, that are adapted to convert electromagnetic radiation into electrical signals. However, as the pixel size decreases, the imager's sensitivity is reduced and crosstalk among pixels is increased.
Today, the predominant type of photodiodes (PDs) are built on planar technology by a process of etching and depositing a number of layers of oxides of silicon, metal and nitride on top of crystalline silicon. The PN junction is constructed as a plurality of layers on a substrate giving a device with an essentially horizontal orientation. The light-detection takes place in a subset of these layers.
Light pipes have been introduced into solid state image devices to confine and transmit electromagnetic radiation impinging thereupon to the photosensitive elements.
The development of nanoscale technology and the ability to produce nanowires has opened up possibilities of designing structures and combining materials in ways not possible in planar technology. For example, in US Publication No. 20040075464 by Samuelson et al, a plurality of devices based on nanowire structures are disclosed.